Nonwoven fabrics are desirable for use in a variety of products such as bandaging materials, garments, disposable diapers, and other personal hygiene products, including pre-moistened wipes. Pre-moistened wipes are often packaged as discrete wipes in a stack in a moisture proof container, and are often referred to as wet wipes. Wet wipes are commonly used as baby wipes for the cleaning of a baby's skin during a diaper change.
Nonwoven fabrics having high levels of strength, thickness, drape, and softness are desirable for body-contacting articles, such as linings for disposable diapers and wet wipes. However, optimizing all the desirable properties is often not possible. For example, often a balance of properties results in less than desirable softness or strength levels. Wet wipes used as baby wipes, for example, should be strong enough when wet to maintain integrity in use, but soft enough to give a pleasing and comfortable tactile sensation to the user(s). In addition they should have fluid retention properties such that they remain wet during storage, and sufficient thickness and porosity to be effective in cleaning the soiled skin of a user.
Strength in a nonwoven fabric can be generated by a variety of known methods. If thermoplastic fibers are used, strength can be imparted by melting, either by through-air bonding or by hot roll calendaring. Hydroentangling fibers in a spunlace operation and adhesive bonding are also commonly used to bind fibers to increase the strength of the nonwoven. However, these processes, while increasing the strength of the nonwoven, generally detract from other desirable properties. For example, thermal bonding is effective at maintaining the thickness (bulk) of the nonwoven, but maintaining a relatively soft product suitable for wet wipes requires the use of relatively expensive conjugate fibers throughout the nonwoven web. The use of conjugate fibers throughout the nonwoven can also negatively affect the drape of the resulting material.
Hydroentangling a fibrous structure generates strength, but typically reduces the thickness of the material. Such a reduction in thickness is undesirable in a wet wipe application. Due to the nature of cleaning tasks for which wet wipes are used, consumers prefer a wipe that has a minimum amount of apparent bulk, or thickness associated with it. To increase the basis weight of the starting material such that after hydroentangling the material retains sufficient thickness to be used as a baby wipe would be prohibitively expensive.
Adhesive bonding can be used to generate sufficient strength, especially in a carded web. However, adhesive adds to the expense of the resulting web, often costing more than the fibers of the base web to which it is applied. Additionally, the presence of adhesive can negatively impact the fragrance and preservative ingredients in a wet wipe. Adhesive application systems also add cost and complexity to a nonwoven manufacturing process, as well as creating hygiene problems in the application equipment and other equipment in the vicinity. Finally, adhesive can contribute to the stiffness of the final nonwoven, which lowers the drape and perceived softness of the material.
In addition to the attributes of relatively high strength, drape, and softness, another property desirable in a nonwoven suitable for a wet wipe is relatively low linting. Linting, or pilling, occurs as fibers, or small bundles of fibers, are pulled off, or otherwise released from, the surface of the nonwoven substrate of the wet wipe. Linting results in fibers remaining on the skin of the user, a highly undesirable condition for wet wipe users. Linting can be controlled in much the same way that strength is imparted. That is, to the extent that fibers of the nonwoven are bonded to, or entangled with, one another, linting levels can be controlled. Therefore, by increasing the level of adhesive in a carded web, for example, linting can be decreased. However, as mentioned above, the increased level of adhesive contributes to greater stiffness and decreased levels of softness.
Accordingly, it would be desirable to have a soft, thick nonwoven web suitable for use as a wet wipe, and having suitable strength to maintain structural integrity during use.
Additionally, it would be desirable to have a soft, thick nonwoven web suitable for use as a wet wipe for effective skin soil cleaning.
Additionally, it would be desirable to have a thick and soft nonwoven web suitable for use as a wet wipe exhibiting relatively low levels of linting without the use of stiffness-increasing additives, such as the addition of adhesive.
Additionally, it would be desirable to have a nonwoven web suitable for a wet wipe that exhibits relatively high retention of fluids such as aqueous fluids, and relatively high strength, but remains soft to the skin, with sufficient thickness, texture and porosity for effective skin soil cleaning.
Finally, it would be desirable to have a nonwoven web, suitable for a wet wipe that can be made with a relatively high strength, thickness and softness, without linting, and can be made economically.